Internet Technologies

We introduced data structures, ways to organize how we store bytes in the memory of a computer, so we can access our data in different ways.

We also talked about algorithms and how to compare their efficiency with big O to measure running time in terms of n, where n is some measurement of the size of a problem.

Searching is much faster with sorted data, but sorting data in itself is a problem that can be solved in different ways.

Data structures we looked at included:

The internet is a network of computers connected together, and we generally think about it in terms of websites and applications, but every time we visit a website, our computer (or device) makes a connection to another computer.

Let’s say we want to visit facebook.com. Our browser actually automatically completes it to http://www.facebook.com/.

We can think of protocols, like HTTP, as humans greeting each other with handshakes, since there is a series of steps that each side follows, according to certain predefined rules.

In Chrome, we can see that with View > Developer > Developer Tools:

Now, if we open the Network tab there and visit https://facebook.com, we’ll see all the requests our browser makes for the page. In this case, there are 52, and the very first one is for the actual page, which includes all the other files:

If we click on that first request, we see many headers that our browser sends:

Each computer on the internet also has an IP (Internet Protocol) address, which is like an address we might write on a real envelope. That address allows messages to be sent and received by the right computers. And websites like facebook.com are just mappings of names that we can remember, to numeric IP addresses of servers that can respond.

In this case, David isn’t logged in, but if he had logged in, Facebook would be able to know who he is based on the cookie header that our browser includes with its request. A cookie is like a digital handstamp, usually a long random string, and each time our browser sends that to the server to verify who we are. Advertisers can also add cookies to their websites, or pieces from their websites that are included in other people’s websites, which allows them to track people visiting different websites. (Adblockers or other browser extensions can prevent this, by refusing those cookies from advertisers.)

To use certain services, we have to make these cost-benefit analyses:

With an Incognito window, our browser doesn’t keep any of the cookies it gets, but our IP address is still revealed (out of necessity).

Our ISP, or internet service provider, also knows what we do on the sites we visit, unless we use HTTPS.

We can also type commands into our computer’s terminal to see this:

And if we try to follow that, we’re sent to the www address:

Now finally, if we make a request to that address, we get a status of OK:

Other HTTP status codes include:

We can see this in the browser too. If we try to visit some random URL for facebook.com that doesn’t exist, we see the response code for the request is 404:

Some years ago, Verizon and other cellular providers were found to be injecting a tracking header into requests made by your phone, so that other companies can track you, a business decision to sell data for profit, made possible by this technical feature.

A VPN, virtual private network, connects you to some other server, through which all your traffic goes. So the outside world will only see the VPN’s IP address, and not be able to track you as easily.

IP, Internet Protocol, is the procedure by which computers on the internet communicate with each other. Every computer on the internet has an IP address, in the format ###.###.###.###. Each number must have a value between 0 and 255, so to represent 256 values we need 8 bits for each number, and thus a total size of 32 bits, or 4 bytes, for an IP address. That also implies a total of only 4 billion IP addresses, and there’s actually a replacement version, IPv6, which assigns addresses with 128 bits, allowing for a lot more addresses.

DHCP, Dynamic Host Configuration Protocol, is the procedure by which a device gets an IP address when it first connects to the internet. It first connects to the local network with a temporary address, and then asks the local DHCP server for an address that it can use.

DNS, Domain Name System, is another system by which domain names are translated to IP addresses. There are root DNS servers that point to other DNS servers (for example, the one for all .com domains) in a hierarchy that eventually gives us an official IP address back for any registered domain.

Our computers might cache an IP address locally, and our ISPs (Internet Service Providers) too might cache all the common domains, to speed up future requests. And an ISP could have DNS servers with fake or nonexistent records for IP addresses for certain domain names.

We can run another program called traceroute:

There is an animation of undersea cables that connects continents across oceans.

We can think of these physical network of cables, and IP in general, as some infrastructure we can abstract away. We can write our software knowing that it’s available, and use the internet not just to send bytes between computers, but have more useful applications.

QoS, or Quality of Service, is another concept where routers might limit or slow how much data you can send and receive of a certain type, in order to prioritize applications like videocalling or realtime games.

If we were to send a large file, it would first be broken up into smaller chunks. Each of those chunks would include additional metadata like 1 of 4 or 2 of 4, which allows the recipient to reassemble them correctly. And if the recipient somehow did not receive a piece, they can request for that missing piece to be sent again. TCP is the protocol that allows that.

Servers can also support other services, such as SSH (secure shell) or SMTP (for sending email). Each of these services also run on some port, or a number added to the end of an IP address in each request, so that the operating system can forward the request to the right service.

We take a look at a few clips, where TV shows use technical terms in sometimes inaccurate ways, to portray hacking or the like.

Now that we know the fundamentals, hopefully we can understand other related concepts. Next time we’ll look at web design!